Orthogonal Frequency Division Multiplexed (OFDM) transmission schemes are widely used in digital communications, including wireless networking (e.g., OFDM is used in the IEEE 802.11 wireless local area networking standards), television and audio broadcasting, and internet access. In an OFDM scheme, the overall system bandwidth is partitioned into a number of orthogonal subcarrier frequencies, commonly referred to as tones. A stream of informational bits is converted to a series of frequency-domain symbols, and these symbols are transmitted over the subcarrier frequencies. Each subcarrier is modulated with a modulation scheme, such as quadrature amplitude modulation (QAM) or some form of phase-shift keying (PSK).
Many techniques have been proposed to transmit pilot signals along with OFDM signals to allow receivers to estimate channel characteristics. One option is to add a distributed pilot channel probe to OFDM data being transmitted. In this approach, the transmitted sequences that constitute the data-bearing OFDM signal and the distributed pilot are conveyed through the transmission channel and typically arrive at the receiver perturbed by multipath effects and Additive White Gaussian Noise (AWGN). The receiver must equalize this received signal before demodulation to counteract the effects of channel multipath.
Minimum mean square error (MMSE) channel estimation techniques have been developed that require extensive matrix manipulations and perfect knowledge of both cross- and auto-covariances. Least-square (LS) channel estimation techniques avoid the requirement for perfect covariance knowledge, instead relying upon non-linear iterative techniques such as least mean square (LMS) and recursive least squares (RLS) to converge upon solutions. Accordingly, there remains a need for a simplified channel estimation solution that allows recovery of the data-bearing OFDM signal by taking advantage of the characteristics of a distributed pilot signal to accurately estimate the transmission channel.